1. Field of the Invention
The invention relates to a method for determining the speed of a vehicle equipped with at least one surround sensor that determines environment data of the vehicle relative to at least one motionless object, and to a device for carrying out this method.
Surround sensors shall be understood to mean detection devices that use measurements to detect and map a vehicle's surroundings. The environment data output by the surround sensor describes objects detected by the measurements relative to the driver's vehicle. Thus, the environment data contains in particular a piece of information about a relative distance between the vehicle and the detected object, if applicable also in the form of a directional relative distance referred to a preferred direction defined by the vehicle. The environment data derived from the measurements can also be the relative distance to the vehicle, the radial velocity and the angle between the vehicle and the motionless object or other parameters that are derived from the measurements and characterize the location of the object relative to the vehicle.
2. Related Art
In order to determine the speed of the driver's vehicle, it is already known to estimate the instantaneous speed from measurements made by vehicle dynamics sensors in the vehicle. The sensors used in such solutions measure, for example, the wheel speed, yaw rate, transverse acceleration, steering acceleration or the steering-wheel angle, and work autonomously. Alternatively, the speed of the vehicle can also be determined from position data that has been determined using a preferably satellite-based navigation system such as Galileo, Glonass or GPS.
It is also known to use suitable sensors to monitor the surroundings of a vehicle. US 2010/0017128 A1 proposes a system for estimating vehicle dynamics. In this system, surround sensors provided in the vehicle for this purpose, such as radar, lidar or camera sensors, detect a stationary object in the vehicle surroundings and track the motion thereof. The speed and position of the vehicle are then estimated from this data, where vehicle motion sensors such as acceleration sensors or wheel speed sensors can also be used. The position and speed of the vehicle, however, can be estimated only relative to the stationary object currently under consideration.
WO 2006/063546 A1 describes a method and device for determining the vehicle speed from at least two images that have been recorded successively in time by a camera of the vehicle. The change in the position and/or the size of an object contained in the images is analyzed in this process. The speed of the vehicle in relation to the object is determined therefrom. The object may be a part of a road marking, for instance.
US 2006/0020389 A1 describes a system for generating digital lane markers in order to display the lane of a vehicle which comprises a camera, a GPS coordinate receiver and a gyro sensor. This data is combined in order to establish the precise position of the vehicle on a traffic lane.
Owing to the fact that the position and/or speed of the vehicle is determined relative to the objects located in the vehicle surroundings and detected by sensors, the values obtained are known only relative to the vehicles and also contain errors. In addition, determining the values takes a relatively long time because it is necessary to track the objects and then analyze this tracking. In addition, satellite data for determining the position of the moving objects is often not available reliably, especially in built-up environments containing streets of high-rise buildings, with the result that determining in particular the position value is difficult and prone to major errors.